Julius Randle backed up his big words and Christmas promise.

After Monday’s disaster against the depleted Wizards, Randle was extremely vocal, saying the Knicks had a “terrible approach to the game” from the morning shootaround on and asked his teammates, including himself, to “look in the mirror’’ over Christmas.

Thursday, Randle was unstoppable on offense and became part of a Knicks defense that throttled the Nets into a 26.9 percent shooting night as Mike Miller’s group posted a stunning 94-82 rout at Barclays Center.

Randle, the $63 million man, racked up 33 points and hit a career-high five 3-pointers on nine attempts, finishing 14 of 26 overall, with eight rebounds.

“I did [look in the mirror],’’ said Randle, who has experienced an up-and-down first season with the Knicks. “I can’t speak for nobody else. I did. What can I do better, how can I be a better leader and better player and be better the next game? I can’t speak for everybody, but top to bottom as a team, we did a great job coming in here and playing great basketball for 48 minutes.”

There was some holiday cheer in the usually depressed Knicks locker room.

“Coaches gave us a great game plan, we had a mental sharpness and focus to us from start to finish,’’ Randle said. “Proud of my guys.’’

There were panicky signs after Monday’s game that players had started to tune out Miller, who moved to 4-6 as interim coach with Thursday’s win. Randle and others talked about a lack of focus at the morning shootaround Monday.

After getting Christmas Day off, Miller staged a secret, two-hour shootaround at Barclays — a length that is unheard of. It did the trick.

“It was a long-ass shootaround,’’ said Marcus Morris, who returned from a one-game absence with a sore Achilles to pump in 22 points after missing his first six shots. “We had to be focused. Because everything we did wrong, we did it again. We came out and they scored 80 points.’’

In scoring 20 first-half points, Randle helped the underdog Knicks to a 46-41 lead by intermission and they pulled away in the second half, going up by as much as 23.

As two-way G-League point guard Kadeem Allen bounced away the final seconds, a large throng of Knicks fans stood up and roared as the club moved to 8-24.

The Knicks are 4-2 when Randle scores 24-plus points. Randle put up 35 points in the loss to the Wizards, but the defense was horrible. In Brooklyn, the band stifled the Nets into posting their lowest shooting percentage since 2012.

“We executed [the defensive plan],’’ Randle said. “We were sharp. To hold that team to 80 points — 14 points in the paint — that’s really good. It was a complete basketball game.

“I’m getting in a good rhythm. Catching the ball in good spots. Teammates are doing a great job of finding me. I’m being patient and taking what the defense gives me and trusting the work I put in.’’

Earlier this season, Randle’s 3-point shot was a mess, dropping below 20 percent. Since Miller took over, Randle is shooting 45 percent from the field — 30 percent from 3-point land.

Things are indeed clicking more from deep for the lefty power forward.

“It can’t rain forever, bro,’’ Randle said. “Can’t rain forever, dog. It’s going to fall eventually.’’